Several patents and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents and publications is incorporated by reference herein.
Bitumen is widely used in binders for mineral aggregates in the pavement construction and roofing industries, since bitumen is hydrophobic and has good adhesion and weathering characteristics. Examples of pavement constructions are surfaces intended to provide a carriageway or hard standing for vehicles, e.g. roadways, car parks, airport runways and the like. Bituminous mixtures used for pavement construction and roofing applications are mainly mixtures of inert materials and bitumen. These bituminous mixtures are also known as asphalt, asphaltic mixtures, asphaltic mixes and agglomerates.
During normal use under the weight of traffic and weathering conditions, however, pavement constructions tend to show distress from several causes, including temperature induced permanent deformation or rutting, low temperature induced thermal cracking and load associated fatigue. While mineral aggregates are the major portion of the paving composition, the bitumen-containing binder provides important properties to the mixture. For this reason, it has been a common practice to improve the pavement constructions' mechanical properties and their resistance to various environmental conditions by adding fibrous reinforcing materials, surfactants or polymers to bituminous mixtures. For example, U.S. Pat. No. 6,866,712 describes a bituminous mix for road pavements that comprises bitumen, mineral aggregates and glass filaments as fibrous reinforcing material.
Polymers used to modify bitumen or asphalt can be non-reactive polymers that do not react with the bitumen or asphalt, such as for example ethylene acrylate or vinyl acetate copolymers, styrene polybutadiene or isoprene, ethylene butadiene block copolymers (e.g. SBS, SIS, SEBS copolymers), polyurethane or polyolefins. Alternatively, the modifier may be a co-reactive polymer, such as for example an epoxy-containing polymer (see for example U.S. Pat. No. 6,743,838) or an anhydride-containing polymer (see for example U.S. Pat. No. 7,157,508).
Since polyvinyl butyral (PVB), whether plasticized or plasticizer-free, cannot be homogeneously mixed with molten bitumen, but rather merely forms heterogeneous mixtures, modifications have been developed to improve the homogeneity of the PVB in the bitumen mixtures. For example, adhesion promoters have been developed to overcome such non-homogeneity problems. Nevertheless, many adhesion promoters are aggressive and toxic chemicals. Therefore, this solution is not environmentally friendly.
U.S. Pat. No. 5,360,848 also describes a modified bitumen. The modification includes adding plasticized PVB and also polyalkylene glycol dialkyl ethers and optionally polystyrene as solubilizing agents to bitumen. This modified bitumen can be further mixed with aggregated minerals to provide bituminous mixtures useful as construction materials for road surfaces. In addition to the costs of the chemical solvents and chemicals, however, this solution is also environmentally unfriendly due to the out-gassing of volatile organic compounds that may also be toxic. Additionally, the volatile solubilizing agent does not solve the compatibility issue for the full length of the expected lifetime of the bitumen products.
In this connection, it is apparent that a paving construction that includes recycled materials is also more environmentally friendly. A considerable amount of polymer waste is produced from both domestic and industrial sources. For example, over 100 million m2 of laminated glass are annually produced in countries of the European Union (EU), mostly from the automotive and the construction industries. In spite of attempts to increase the direct recycling of polymer waste, most plastics are currently incinerated or disposed in landfill sites, which is not only problematic from an environmental perspective but is also very expensive. The legislations of many countries in the world are motivating an environmentally friendly waste disposal of laminated glass through “end of life vehicles” approach. For example, EU directives 2000/53/EC and 91/156/EC force the European Union member countries to minimize landfill waste. As a result, glass has to be recycled to a considerable extent. Separated plastics, however, are currently not re-usable for industrial applications and are incinerated or land-filled.
Asphalt/bitumen modification with waste polymers is a remediation technology that has been developed to overcome such problems. The process consists of binding polymeric material that may be contaminated in a stable product, reducing leaching of contaminants to the environment. Recovered or recycled PVB may be obtained from various applications such as for example from laminated glass used for windows in buildings and vehicle windshields, in which plasticized PVB is used as an energy absorbing interlayer between two glass sheets.
Finally, U.S. Patent Appln. Publn. No. 2006/0075928 describes asphalt compositions that are suitable for use in the construction of roads. These asphalt compositions comprise bitumen and a dry portion comprising up to 50 wt % of a plastic material, coarse aggregates and fine aggregates. The plastic material is randomly distributed in the mixture, thus contributing to high viscosity and heterogeneous mixtures. For these reasons, the mechanical properties of the mixtures during the paving process and during the lifetime of the road are difficult to predict.
There remains a need for improved bituminous mixtures having enhanced properties. There is also a need for bituminous mixtures that can be manufactured using a streamlined process that is more economical or more environmentally friendly than conventional techniques.